The song is a self-addressed warning, and its whole art is that the warning is useless. Dil sambhal ja zara: steady yourself, heart, just a little. The zara is the giveaway. It is the particle you use when you still believe a little will be enough, and the song's other repeated line answers it: the heart is about to do the thing anyway. The structure is a man watching his own defeat in advance.
The opening passage explains why the defeat is certain. Every time he came near her he found peace, sukoon, and more: he found the existence, wajood, he had been busy forgetting. The song's first confession is that forgetting her was work, and the work was failing. Then the two lines that map the whole geography of need: when the season of grief came, he remembered her. When the loneliness itself frightened him, he remembered her. Grief and fear are the two roads, and both lead to the same address.
The refrain is the warning, and the warning keeps losing to the evidence. Aisa kyun kar hua, jaano na, main jaano na: why did it happen this way, I don't know, I just don't know. The ignorance is not a confession of stupidity, it is the exact state of a person watching themselves repeat a pattern they have already fully mapped. Knowing the mechanics of your own fall does not stop the fall. The song is built on that, and it is why it rings true.
The second verse catches the ordinary life of a longing. The road that passes her house, and how often he has walked it, on purpose, while telling himself it was on the way. Shayad yahi dil mein raha: perhaps this stayed in the heart, the hope that she might appear, who knows. The hope is tucked inside the word shayad, perhaps, the way actual hope always is.
The last verse states the case in its bare form. Nothing between them, nothing at all, kuchh bhi nahin jab darmiyaan, and still the heart keeps weaving her dreams. He tried to forget her, and even that was not possible, and the word the song uses for the attempt, chaha ki de tujhko bhula, carries the whole failure in its grammar. The song ends on the warning again, which means it ends exactly where it began, which is what falling in love again means.
The recording splits the verses between three voices, which suits a song that is really a committee inside one person. Mohammed Irfan, Arijit Singh and Saim Bhat each carry a passage, and Mithoon's arrangement keeps the whole thing quiet enough that the words stay in charge.